The present invention relates to a printer in which a print head of e.g. a dot-matrix type is mounted on a carriage and opposed to a platen so as to be movable along a print line for printing operation.
Generally, in printers of this type, a machine frame supporting the platen, carriage and other components is fabricated by bending a metal plate material into a predetermined shape by pressing or the like. The components are mounted on the frame by welding, screwing or other suitable methods.
Thus, in the manufacture of the prior art printers, sheet metal processing for the frame and assembly of the components thereon require much time and labor, lowering working efficiency. Also, the dimensional accuracy of the frame and assembled components is subject to increased variations, and the frame, made of metal, is inevitably heavy in weight.
Since the accuracy of the gap between the platen and the print head opposed thereto, that is, printing gap, greatly influences the print quality of the printer, the frame needs to have a strength high enough to minimize flexure and torsion. In this regard, the metallic frame may provide a measure of strength. However, if a thinner metal plate is used for the frame with the aim of reducing the gross weight of the printer, to meet the needs of the times, reinforcing plates may sometimes be required to insure adequate strength. Thus, the manufacture of the frame takes more time, and it would be impossible to effectively reduce the printer weight.
For the reduction of the frame weight, synthetic resin or plastic material may possibly be used for the frame, in place of the metal material. A plastic frame, however, lacks mechanical strength and cannot be put to practical use in printers.
When manufacturing the printer frame of the aforementioned type with use of a plastic material, therefore, it is necessary to provide a considerably thick structure to resist flexure or torsion, or to reinforce the frame structure with metallic reinforcing members. Even so, the proposed improvement still involves the same problems of the metallic frame, such as increased weight and low working efficiency.
The frame strength also depends on protection of the components of the printing mechanism assembly, such as the print head and platen, against the impact of vibration or other external forces. During the printing operation, moreover, the impact of the print head will cause vibration, which will be transmitted to the frame producing noise, or to a table carrying the printer giving the operator an unpleasant sensation. This would lead to distortion of the components of the printer or loosening of fixing screws, possibly lowering the print quality or causing premature trouble with the printer.